1. Field of the Invention
This invention generally relates to electron beam deflection circuits for a television receiver and the like, and more particularly is directed to an improvement in vertical deflection circuits of the type having an output stage in the configuration of a single-ended push-pull amplifier.
2. Description of the Prior Art
In television receivers and the like, it is necessary to deflect an electron beam in a cathode ray tube employed therein to display reproduced images thereon. To achieve the required beam deflection, various kinds of circuits have previously been proposed as vertical and horizontal deflection circuits. One of those vertical deflection circuits has an output stage, in the form of a single-ended push-pull amplifier, which supplies sawtooth wave vertical deflection current to a vertical deflection winding. Such a circuit has been often employed, usually in the form of a transistorized circuit, because it is suitable for supplying a relatively large current to a load. However, previously proposed vertical deflection circuits having the output stage in the form of a single-ended push-pull amplifier were unable to avoid a certain amount of useless power consumption which is inherent in the circuit construction and, therefore, the efficiency, namely, the ratio between the output power at the vertical deflection winding and the power supplied to the circuit, is relatively poor. Some circuits of the described type have also been proposed with the intention of providing an improvement in the power consumption, but none of them seem to have obtained fully satisfactory results.
With a sawtooth wave current circuit as a vertical deflection circuit of the single-ended push-pull amplifier type, first and second active elements or transistors are connected in series between both terminals of a power supply source and a load coil (deflection winding) is connected to the connection point between the first and second active elements. A sawtooth wave current is passed through the load winding as a result of a current which will pass through the first active element to the load winding in a first direction during the former or initial position half period of a respective input sawtooth wave signal applied to the active elements (the former half period of the retrace period of the sawtooth wave current) and a current which will pass through the second active element to the load winding in a second direction during the latter or negative half period of the respective input sawtooth wave signal (the latter half period of the retrace period of the sawtooth wave current). Accordingly, the current passed through the load winding has to be reversed in direction at every wave of the input sawtooth wave signal. In order to cause the flow through the load winding of a current whose direction is reversed at every wave of the input sawtooth wave signal as described above, it is necessary that, in such sawtooth wave current circuits a voltage which is sufficiently high with respect to one of the voltage source terminals be supplied to the other of the voltage source terminals. If it is assumed that such voltage which sufficiently high, as described above, is always supplied to one of the voltage source terminals, the power consumption, which is the product of the current flowing through the first active element during the former a positive half period of each wave of the input sawtooth wave signal and such high voltage, becomes relatively high.
In the described sawtooth wave current circuit, the sufficiently high voltage, which is required to be applied to one of the voltage source terminals as mentioned above, is to ensure that a current whose direction is reversed at every wave of the input sawtooth wave signal will be passed through the load winding. Therefore, it is enough that the sufficiently high voltage is obtained only at the transition from one wave of the input sawtooth wave signal to the following wave thereof (that is, during the retrace period of the sawtooth wave current). Accordingly, the relatively large power consumed by the first active element during the former or positive half period of each wave of the input sawtooth wave signal is wasted or has no useful purpose. Therefore, it will be seen that, if one of the voltage source terminals is supplied with a relatively low voltage during the former or positive half period of each wave of the input of the input sawtooth wave signal and with the above mentioned sufficiently high voltage only during the latter or negative half period thereof, the consumed power is reduced and hence the efficiency can be improved as a whole.